The present invention is related to ultraviolet radiating apparatus which are used to cure solvent-free ink which has been applied to a substrate by printing or coating. More particularly, the invention is directed to improvements in apparatus of the type generally shown by U.S. Pat. No. 3,733,709 issued May 22, 1973 to Bassemir et al. and U.S. Pat. No. 3,829,982 issued to Pray et al. on Aug. 20, 1974.
The prior art apparatus cited is directed to means for radiating ultraviolet (UV) light against non-solvent inks or coatings which have been applied to the surface of a substrate. The substrate may be comprised, for example, of material such as paper, fabric or thin metal sheets in continuous lengths which can receive the non-solvent ink and which can then be continuously passed beneath UV radiation means comprising a plurality of parallel elongated lamps which extend transversly to the direction of movement of the printed substrate. The ultraviolet light causes a reaction in the ink which permits it to cure. Use of such non-solvent inks has been found to be very useful in that they avoid the problems of air pollution caused by evaporating solvents used in traditional inks.
The use of non-solvent inks and UV lamps have, however, presented drawbacks which have heretofore been unsolved. It is often desirable during the printing process to halt the progression of the substrate thereby subjecting a portion of it to the radiation of the UV lamps for an extended period of time, but the UV lamps generate substantial quantities of heat which may rapidly damage or destroy the substrate if it is not continuously moved past the lamps. It is not feasible to merely shut-off the lamps because they generally require at least 5 to 10 minutes to be restarted if the power is decreased by more than 50%. None of the prior apparatus have presented an effective, uncomplicated method of protecting the substrate against continued radiation in the event it is temporarily halted.
The prior art apparatus also fails to present means to permit high speed printing and curing of the non-solvent ink. The lamps used to produce the UV radiation emit light varying from zero to a maximum value at a frequency of 120Hz and generally include a reflector which focuses the light emitted onto an area of the substrate comprising a strip approximately 1/2 inch wide. Therefore, if the ink is passed through the band of radiation at a high rate of speed the intensity of UV light contacting various areas of the ink will vary and the amount of curing will also vary.